如何在区块链中解密？

Question

I have been asked to use BlockChain for a web app I am building and I did not hear about it before, after searching some information about it, now I understand what it is about. So, basically it encrypts some data in blocks and in this way, the data is safe.

For instance, I have this code I took from internet:

const SHA256 = require('crypto-js/sha256')

class Block {
    constructor(timestamp, data) {
        this.index = 0;
        this.timestamp = timestamp;
        this.data = data;
        this.previousHash = "0";
        this.hash = this.calculateHash();
        this.nonce = 0;
    }

    calculateHash() {
        return SHA256(this.index + this.previousHash + this.timestamp + this.data + this.nonce).toString();
    }

    mineBlock(difficulty) {

    }
}

class Blockchain{
    constructor() {
        this.chain = [this.createGenesis()];
    }

    createGenesis() {
        return new Block(0, "01/01/2017", "Genesis block", "0")
    }

    latestBlock() {
        return this.chain[this.chain.length - 1]
    }

    addBlock(newBlock){
        newBlock.previousHash = this.latestBlock().hash;
        newBlock.hash = newBlock.calculateHash();
        this.chain.push(newBlock);
    }

    checkValid() {
        for(let i = 1; i < this.chain.length; i++) {
            const currentBlock = this.chain[i];
            const previousBlock = this.chain[i - 1];

            if (currentBlock.hash !== currentBlock.calculateHash()) {
                return false;
            }

            if (currentBlock.previousHash !== previousBlock.hash) {
                return false;
            }
        }

        return true;
    }
}

let jsChain = new Blockchain();
jsChain.addBlock(new Block("12/25/2017", {amount: 5}));
jsChain.addBlock(new Block("12/26/2017", {amount: 10}));

And this is the result:

As you can see, we have encrypted "Genesis block" in blocks (if I am not wrong).

Ok so, what if I want to decrypt the data in order to get "Genesis block" back? Will this be possible?

I am new at this, so I find it a bit confusing... I understand what it is about but I do not know how I would implement it to my web app. My web app basically gets some information from the database, shows that information to the final user and the final user sends an email to a customer who will have to pay through a link.

Answer 1

Blockchains are not about encrypting data to keep it "safe"; they are about creating an auditable ledger of changes to some state that needs to be agreed by multiple parties. In the case of bitcoin, they represent the distribution of currency across different wallets, and record transactions which change that distribution.

Blockchains are a very specialized technology, and while there are a few situations where they are useful, there are also a lot people searching for problems to fit the solution. You're better off analysing your actual problems first, and then looking around for technologies that solve those problems.

In this case, your number one priority should be general security - if someone manages to run an UPDATE on your internal database, something has already gone very wrong. As part of "defence in depth", you might also want an audit trail of changes that have been made. That might mean picking a database technology that forms an append-only ledger, but unlike a traditional blockchain, you probably don't need that to be based on distributed consensus. And you might find that actually having a separately secured audit log that you can cross-check if anything suspicious happens is enough for the scenarios you're expecting.

Finally, if you do decide that a blockchain-based ledger solves a real problem you have, look for an existing implementation you can take advantage of, for the same reason you wouldn't try to write MySQL from scratch.